VDJ Pro! if you like to get technical with few limitations and can stand an almost complete software which has more features than any other competitor (VDJ8 will hopefully bring all these features together for novice users).
Traktor if you like a little modification and are happy with the quality of NI gear because nothing else will work with it properly,
Intro if you are just wanting plugin and play two tracks.
VDJ LE is the worst LE software as the eq is terrible, the mapping is always basic and the effects are shockingly bad in quality… You should contact numark to see if they give you a different serial, I remember someone on the vdj forum saying they were able to do that a while ago. It will be essential if you choose to go with VDJ as it gives you 50% off which is just over $150…